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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>

        function Ready(){}
        Ready.prototype.setState = function(){
            this.$button.innerHTML = '准备视频通话';
            this.state = this.callingState;      
            console.log('准备视频通话');              
        }

        function Calling(){}
        Calling.prototype.setState = function(){
            this.$button.innerHTML = '正在视频通话';
            this.state = this.endState; 
            console.log('正在视频通话');            
        }       

        function End(){}
        End.prototype.setState = function(){
            this.$button.innerHTML = '视频通话结束';  
            this.state = this.readyState;
            console.log('视频通话结束');            
        } 

        function VideoCallMethod(){
            this.readyState = new Ready();
            this.callingState = new Calling();
            this.endState = new End();
            this.state = this.readyState;
            this.$button = null;
        }
        VideoCallMethod.prototype.init = function(){
            this.$button = document.createElement('button');
            this.$button.innerHTML = '准备视频通话';
            document.body.appendChild(this.$button);
            this.eventCenter();
        }
        VideoCallMethod.prototype.eventCenter = function(){
            var that = this;
            this.$button.onclick = function(){
                that.state.setState.call(that);
            }
        }

        var v1 = new VideoCallMethod();
        v1.init();
        
    </script>
</body>
</html>